A series of catalysts were prepared by loading titanium dioxide with chromium and different amounts of phosphorus. Investigation in the oxidative dehydrogenation of ethane showed that chromium notably increases the activity of TiO2 principally toward the total oxidation of the hydrocarbon. Addition of phosphorus to the system simultaneously improved the global conversion and the ethylene selectivity. Moreover, a fairly good correlation between the catalysts acidity, the P/Cr ratios and the activity in the ODH reaction was established. It was also found that an excess of phosphorus, although it increases the acidity, decreases the conversion as if phosphorus effect was optimum for P/Cr ratios equal to 1.6. EPR and UV-visible characterizations of the samples before and after the catalytic tests showed that the improvement of the catalysts performances might be due to the isolated octahedral Cr3+ species that appear on the support.